The present invention relates to negative resists having high thermal stability based on oligomeric and/or polymeric polybenzoxazole precursors, as well as to a method for manufacturing highly heat-resistant relief structures from these negative resists.
Hydroxypolyamides are used as soluble polybenzoxazole precursors in high-temperature-resistant photoresists. Such photoresists are needed to directly structure organic insulating layers in a cost-effective manner. The polybenzoxazoles obtained from the hydroxpolyamides are distinguished by high temperature resistance, low water absorption, and excellent electrical properties. The polybenzoxazoles can be used as etching masks, particularly in alkaline etching processes, but they can also be used as organic dielectric materials in semiconductor manufacturing.
Photostructurable polybenzoxazole precursors can find applications in both positive and negative resists. The positive resists contain a photoactive component in the form of a diazoquinone in addition to the polymer precursor (c.f., European Patent 0 023 662, European Published Patent Application 0 291 779 and German Published Patent Application 37 16 629). The negative resists have polymer precursors with cross-linkable, unsaturated groups (c.f., European Patent 0 041 677).
However, storage stability problems can occur for both positive and negative resists. In the case of concentrated positive resist solutions containing hydroxypolyamides, a polycondensation reaction can occur. Negative resists tend to polymerize due to the presence of unsaturated groups, such as acrylic and metacrylic groups. In both resist types, this leads to an increase in viscosity or even to the formation of a gel. Moreover, in the case of positive resists, the photoactive component can be destroyed by terminal alkaline amino groups or by amine monomers and amide oligomers.